Many circuits commonly used in commercial integrated circuits require known resistor values to serve as references to enable accuracy in the circuit function. Example applications for accurate components include oscillators, amplifiers, voltage regulators, current mirrors, current sources, op-amps with feedback, etc. Current techniques for obtaining resistors with known values include screening resistor values, using resistor deltas, using either mechanical or electrical trimming of resistors in a post-production process, and the like. Example applications include tuning and phase locking operations in communications circuitry, current sources, current mirrors, bias currents, and other applications using resistance.
Most resistors produced in semiconductor processes in known prior approaches have an inherent dependence on temperature, and resistors produced in semiconductor processing also depend on process variations. Example resistors include polysilicon resistors and N well resistors formed from N-type doped semiconductor material. These resistors have values that vary with temperature and with process variations. Many techniques have been developed to modify the physical devices to reduce or compensate for temperature variation so the resistors can be used for a reference value or to generate a current from a voltage, for example. However, none of these is available to be incorporated into a practical integrated circuit. The need for accurate voltage and current sources leads to the fabrication of complex circuitry to overcome the prior art resistor temperature and process variations. A “PTAT” (proportional to absolute temperature) circuit can be used in a ratio or divider circuit, with current mirrors and feedback amplifiers for example, to attempt to remove the temperature dependence from a current or voltage. A common circuit is a bandgap reference circuit for producing a reference voltage independent of these variations. A resistor can be used to produce a current from the voltage output by a bandgap reference circuit. The output current is simply the reference voltage divided by the resistance. However, even if the resistance temperature dependence is compensated for by using a ratio or other operation to cancel out the temperature dependent factors, the process variations remain and there is no practical semiconductor process resistor available to date that is a fixed value over all expected process and temperature variations. For example, known prior resistors produced in semiconductor processes have value dependencies that vary with process steps such as lithography, deposition, and etching. The resistor values also depend on variable thin film properties such as film thickness, uniformity, and composition.
A known component with a conductivity value (the inverse of resistance value) that is a fixed quantity has been constructed using a quantum device. Quantum devices have been described in semiconductor processes at room temperature. For example, U.S. Patent Application Publication No. 2012/00098590, titled “Quantum Electro-Optical Device using CMOS Transistor with Reverse Polarity Drain Implant,” with inventors Edwards et. al., published Apr. 26, 2012, which is co-owned with the present application and which is hereby incorporated by reference in its entirety herein, describes forming a quantum device using a CMOS semiconductor process. By creating a confinement quantum well of very small dimensions, e.g., between 5 and 15 nanometers, quantum operations can be achieved in semiconductor material.
A quantum point contact exhibiting quantized conductance in a GaAs substrate is described in a paper titled “Quantum Point Contacts—The quantization of ballistic electron transport through a constriction demonstrates that conduction is transmission”, Physics Today, authored by Henk van Houten and Carlo Beenakker, July 1996, at p. 22. In this prior known approach, a heterojunction is formed between a GaAs substrate and AlGaAs material and a constriction point is formed beneath a gate terminal. A 2D electron gas is formed on either side of the constriction point. A gate conductor overlies the constriction point. When a constriction point for electron transport is similar in width to the Fermi wavelength for the electrons, a quantum point contact is formed. In the paper, conductance (I/V) was found for the quantum point contact that is quantized and proportional to the ratio 2e2/h, where e is the electron charge, and h is Planck's constant, inversely this forms a quantized resistance proportional to h/2e2, or approximately 1/13 kohms. This resistance has a value that depends only on physical constants and is not temperature or process dependent. A series of step values corresponding to quantized conductance controlled by a gate voltage is demonstrated in the paper at near zero temperatures. The conductance is proportional only to 2 physical constants and so an accurate and fixed value resistance or conductance component is possible.
A continuing need thus exists for fixed and stable value passive components such as resistors that can be formed within a current commercial MOS semiconductor process and which operate at room temperature and over commercially acceptable temperature ranges. By fabricating the resistor devices along with MOS devices such as transistors, capacitors, diodes and the like in a single integrated circuit device, control circuitry can be formed alongside and using the resistive devices, forming a commercially useful integrated circuit. Because the resistance will be accurate over temperature and process variations, the need for complex temperature compensation circuitry and other temperature compensated resistor circuits can be reduced or eliminated, saving silicon area and reducing the size and complexity of the integrated circuits.